Re: Object that transfers ownership on assignment/copy

"Victor Bazarov" <>
Wed, 5 Sep 2007 18:28:31 -0400
Scott Gifford wrote:

"Victor Bazarov" <> writes:

Scott Gifford wrote:


   C c_factory() {
     return C(new string("foo"));


Here you have a temporary from which you're trying to construct
an object. That operation requires binding a non-const reference
to the temporary, which is prohibited.

I assume you mean the above snippet? I can fix this particular error
by replacing using a temporary:

   C c_factory() {
     C tmp(new string("foo"));
     return tmp;

The variable you call 'tmp' has nothing to do with the "temporary" that
I refered to. A temporary object and an object with automatic storage
duration are not the same. Your 'tmp' here is the latter. The former
is created as the function returns a value.

but one error still remains:

   test8.C: In function int main():
   test8.C:33: error: no matching function for call to C::C(C)
   test8.C:10: note: candidates are: C::C(C&)
   test8.C:8: note: C::C(std::string*)

Take a look at how 'auto_ptr' is implemented and follow that instead
of trying to wrap it up.

The actual code contains more member variables and methods, so it's
not quite as simple as what I posted. Since the auto_ptr code is
nontrivial and I don't understand all of it, I suspect it would be too
error-prone to try and copy its implementation into my class. I will
probably contine using the "mutable" hack if there's not a
straightforward way to make this work.

In case you don't read my other reply, think reference counting instead
of transfer of ownership.

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